Ethanol production using a wide variety of feedstocks has emerged as an alternative for the replacement of fuels such as gasoline in the transportation and other markets. Feedstocks can include starch-containing agricultural products such as corn, wheat and sorghum sugar-based agricultural products derived from sugar cane, sugar beets, etc.; emerging cellulosic- and lignocellulosic-based biomass from agricultural wastes such as corn stover, rice hulls, and lumber operations, and purpose grown plants and organisms such as switchgrass, Panicum virgatum, Miscanthus, trees, brush, algae, and the like.
For starch based ethanol production, the two most common processes in the U.S.—the dry-grind process and the wet-mill process. Dry-grind facilities represent the majority of the existing corn ethanol plants in the U.S. and most of which can generally be described as utilizing a process in which 100% of the corn's composition is fed to the fermentation process. Dry-grind facilities have the advantages of lower overall capital cost, 100% of the fermentable feed enters the fermentation reactors, and free lipids from the feed in the fermentation liquids functions as an anti-foaming agent. Corn oil can be removed in a dry-grind facility by several methods including up-front fractionation of the incoming ground corn, mechanical separation from various stillage streams, and solvent extraction from dried byproducts.
In wet-mill facilities the corn is preprocessed and fractionated into different components such as the germs, glutens, and fibers prior to the fermentation process. The germ contains the majority of the corn oil contained in the kernel. The corn oil can be obtained by mechanical extrusion of the germ, and/or by solvent extraction. The advantages of the wet-mill process is that additional by-products can be extracted prior to the fermentation process, but the disadvantages are much higher overall capital cost, less than 100% of the fermentable feed enters the fermentation reactors resulting in lower ethanol production per mass of feed, and increased operating costs for anti-foaming agents.
Realization that the fermentation by-product streams have potential value is well known in the industry. As early as the 1940's, U.S. Pat. No. 2,211,604, U.S. Pat. No. 2,221,605, and U.S. Pat. No. 2,263,608 referenced the extraction of animal feed and oil extraction and taught autoclaving of stillage streams to enhance filtration and support downstream solvent extraction. In 1953, U.S. Pat. No. 2,663,718 taught the recovery of oil from distillery stillage using a tri-phase separation centrifuge. This art was again discussed US 2004/0087808 and US 2006/0041152, both of which disclose the recovery of a corn oil co-product from stillage streams of dry grind ethanol facilities using centrifuges. As early as 1911, U.S. Pat. No. 1,147,767 and U.S. Pat. No. 1,147,768 recognized the presence of desirable compounds in waste distillers slop or stillage. In 1993, U.S. Pat. No. 5,177,008 and in its parent applications U.S. Pat. No. 381,179, filed Jul. 18, 1989, and U.S. Pat. No. 136,415, filed Dec. 22, 1987, disclosed a process for the recovery of other desirable compounds including glycerol, succinic acid, lactic acid, and betaine.
With the evolution of the ethanol industry in the U.S., centrifuges are frequently included in the process to recover crude corn oil from the stillage streams as an additional co-product that can be used for higher value animal feed or feed stock for biodiesel or renewable diesel production. Frequently, these facilities recover a small fraction of the available oil, or recover a low quality product which contains an excessive quantity of solids that must be removed downstream with a series of high cost bulk storage tanks functioning as high volume settling tanks or decanters.
U.S. Pat. No. 8,236,977 discloses that stillage may be separated into three or four phases or layers that can form during separation, including free oil phase, light phase, aqueous phase, and solids or bottoms phase. The separation step may be a mechanical step, such as those utilizing differences in density and differences in size, such as decanting vessels, centrifuges, filters, and combinations thereof. Chemical treatment by addition of at least one emulsion breaking additive may be utilized to facilitate separation of oil from the oil-rich material. For example, after the initial separation step, any basic chemical solution may be added to the light phase mixture to adjust the pH and raise the pH to the range of about 6 to 12. The chemical treatment by addition of at least one emulsion breaking additive may be achieved in a single step or in multiple steps using inline static mixers, motorized mixers or batch equipment, and appropriate dosing pumps and/or metering systems. However, the addition of pH adjusting agents, especially neutralizers, may allow soaps to form, such as when adding alkali bases to vegetable oils which contain triglycerides and an undesirable color may be introduced into the final product, due to a Maillard reaction.
Accordingly, it would be desirable to have a method that promotes the separation of oil from the oil-rich phases, such as those in the light phase mixture, to increase the level of oil extracted, without the attendant issues of soaps and discoloration. The present invention is directed to these, as well as other, important needs.